Ethylene-propylene-non-conjugated diene elastomers stabilized with epoxy ester-phosphite mixtures



United States Patent i 3,361,691 ETHYLENE PROPYLENE NON CONJUGATED DIENE ELASTOMERS STABILIZED Wri l H EhOXY ESTER-PHGSPHITE MHXTURES Russell A. Mazzeo, Waterbury, Conn, assigns-r to Uniroyal, Inc, a corporation of New Jersey No Drawing. Filed Apr. 21, 1965, Ser. No. 449,82 6 Claims. (Cl. 260-233) This invention relates to the stabiization of an unsaturated elastomer which is a terpolymer of two different monoolefins, usually ethylene and propylene, and a nonconjugated diene, hereinafter referred to as EPDM. More particularly the invention relates to the use of an epoxidized soy bean oil or an epoxidized ester of a higher fatty acid, in conjunction with an aryl phosphite in an EPDM polymer to impart color stability upon heat aging of the polymer.

Unsaturated EPDM polymer is a particularly difiicult material to stabilize, especially against discoloration upon heat aging. Thus, epoxides such as epoxidized soy bean oil or epoxidized higher fatty acid esters do not prevent this unsaturated polymer from turning yellow and eventually brown upon heat aging. Similarly, tri(alkylphenyl) phosphites do not prevent the unsaturated EPDM polymet from darkening as a result of heat exposure. Individually, the described epoxides or phosphites therefore are not effective stabilizers against undesirable color changes in unsaturaed EPDM upon heat aging.

The invention is based on the surprising discovery that, contrary to what would be expected from the effect of the described epoxide or phosphite individually when the two are combined in unsaturated EPDM terpolymer rubber there is a remarkable synergism and the polymer is rendered highly resistant to undesirable color changes upon heating.

The EPDM employed in the invention is of course a conventional material, and may be defined as a co-polymer of at least two different monooletins (usually ethylene and propylene although other pairs of monoolefins may be employed) with a small amount of at least one copolymen'zable multiolefin. Usually the multiolefin contains from 5 to 22 carbon atoms and has two double bonds separated by more than two carbon atoms. The multiolefin ordinarily comprises from about 0.5 to not greater than about 20 mole percent of the interpolyrner and the ethylene and propylene units are present in ratios from about 1:4 to about 3:1. Examples of suitable multiolefins are straight or branched chain diolefins, such as those in which both double bonds are terminal as in 1,4- pentadiene, l,5-hexadiene(biallyl), 2-rnethyl-l,5 -hexadiene, 3,3-dimethyl-1,5-hexadiene, 1,7-octadiene 1,9-decadiene, 1,19-eicosadiene, and the like; diolefins in which only one double bond is terminal such as 1,4-hexadiene, 1,9-octadecadiene, 6-methyl-L5-heptadiene, 7-methyl-1,6- octadiene, 11-ethyl-1,ll-tridecadiene, and similar compounds in which the internal double bond is shielded. Also suitable are the bridged-ring hydrocarbons of similar nature including endocyclic hydrocarbons containing 7 to carbon atoms and two double bonds especially those containing a methane or an ethane bridge, for example: (a) unsaturated derivatives of bicyclo[2,2,1] heptane containing at least two double bonds, including bicyclo [2,2,1] hepta-2,5-diene; dicyclopentadiene (also named 3a, 4, 7a-tetrahydro-4,7-methanoindene), tricyclopentadiene, and tetracyclopentadiene; (b) unsaturated derivatives of bicyclo[2,2,2] octane containing at least two double bonds, including bicyclo[2,2,2] octa-2,5-diene; (c) unsaturated derivatives of bicyclo[3,2,l] octane containing at least two double bonds; ((1) unsaturated derivatives of bicyclo[3,3,1]-nonane containing at least two double bonds; (e) unsaturated derivatives of bicycle Patented Jan. 2, E953 [3,2,2] nonane containing at least two double bonds, and the like. Preferred are dicyclopentadiene, 1,4-hexadiene, and methylene norbornene.

The epoxides employed in the invention are substantially soluble in hydrocarbon solvents (eg. hexane), substantially insoluble in Water, do not boil at temperatures normally encountered in processing EPDM, and are selected from the group consisting of epoxidized soy bean oil and epoxidized higher fatty acid esters, typified by esters of C to C fatty acids with alkanols having up to 10 carbon atoms (e.g. methyl alcohol, octyl alcohol, decyl alcohol, and the like). Examples of commercial types of epoxidized soy bean oil are such materials as Paraplex G-60, G-6l, G62 and Flexol EPO, which have an average molecular weight of 1000 (see, for example, U.S. Patent 2,829,135). Epoxidized higher fatty acid esters are represented by such commercial materials as Drapex 3.2, octyl epoxy stearate having a molecular weight of 410, or Monoplex S71, an epoxidized oleate ester with an average molecular weight of 380. Epoxide contents in such materials frequently run from about 2% to about 10%' The aryl phosphite employed in the invention along with the described epoxide, is typically a triaryl phosphite, especially a triphenyl phosphite in which the phenyl groups are substituted with alkyl radicals, preferably higher alkyl groups (e.g., (I -C as described in US. Patent 2,733,226, Hunter, January 31, 1956. Examples are tri(o-octylphenyl) phosphite, tri(p-nonylphenyl) phosphite, tri(p-dodecylphenyl) phosphite, tri(diuonyl phenyl) phosphite, mono(nonylphenyl) di(octylphenyl) phosphite, tri(niixed nonylated phenyl) phosphite and the like.

For purposes of the invention there may be employed from 0.1 to 1.0 phr. (parts per hundred of rubber, by Weight) of the described phosphite and from 0.5 to 5.0 phr. of the described epoxide, provided that the amount of epoxide is from 50% to 500% on the weight of the phosphite.

The described epoxide and phosphite may be added to the EPDM polymer at any time at which it is desired to protect the polymer from the adverse efi'ects of aging. Thus, the epoxide and phosphite are suitably added to the solution or cement, in which the EPDM is prepared, at the conclusion of the polymerization reaction and prior to the steps of recovery and purification of the EPDM. The epoxide and phosphite are conveniently added in the form of a solution in an organic solvent, suitably the same solvent as the solvent used in the polymerization reaction, e.g., hexane after the cement is washed. The EPDM is thereafter recovered from the cement in the usual manner, that is, unreacted monomers are removed and catalyst is deactivated. Solvent removal and washing of the polymer, usually with an aqueous medium, are followed by drying of the EPDM, usually at elevated temperature.

While it is not desired to limit the invention to any particular theory of operation, it is believed to be possible that the present epoxide prevents the hydrolysis of the phosphite and also complexes with residual catalyst and other impurities whose efiects are detrimental to polymer color and stability.

It is conventional to add certain epoxides to the tris(alkylphenyl) phosphites of Hunter, US. Patent 2,733,226 to remove traces of acidic impurities, but the epoxides employed for that purpose are dilterent from the presently employed epoxides which are in general higher molec ular weight readily hydrocarbon-soluble and substantially water-insoluble materials, namely, those selected from the group consisting of epoxidized soy bean oil and epoxidized higher fatty acid esters. Furthermore, only a small amount of epoxide (0.1%10% on the weight of the phosphite) is used to remove traces of acidic impurities from the phosphite in prior practice, whereas in the pres ent invention there is employed, as stated previously, from 50% to 500% of specified epoxide n the weight of the portions and to one of the fractions, 1 phr. of Drapex 3.2 may be stirred in. Both samples maybe flocculated by allowing the solvent to evaporate. The solid rubber samples may then be placed in an oven set at 130 C. for

This example illustrates improved color stability in heat aged unsaturated EPDM containing Polygard and Drapex 3.2 (octyl epoxy stearate). A washed 6% solution of EPDM (e.g. ethylene-propylene-dicyclopentadiene terpolyrner; E/P ratio, 70/ 30; iodine number, 12; intrinsic viscosity in tetralin at 130 C., 2.3) in hexane containing 0.5 phr. Polygard may be separated into two phosphite. The trace amount of epoxide added to the comthree hours. The sample containing the epoxide does not mercial tris(alkylphenyl) phosphite is believed to be 65- discolor whereas the sample thatfidid not contain the sentially consumed by reaction with traces of residual acid epoxide turns yellow. The results are shown in Table II. in the phosphite', and/or is subsequently volatilized, so that there would ordinarily be little or no remaining available epoxide in the phosphite. In addition, the conven TABLE H tional practice is to use a relatively low molecular weight, water-soluble material such as propylene oxide to neu- Amounts Addmves (PM) Color After Heat traiize traces of acid remaining in the phosphite; such a Sample s s g g material would be unsuitable for the present purpose, Pmygardn Drapex 3.2-2 3 even if used in sufficiently large amount, because it would 15 be washed out of the EPDM and lost in the water used 0 5 None YeHOw to purify the polymer. The presently employed epoxide 045 Whitematerials are substantially hydrocarbon-soluble, thus facilitating their introduction into the EPDM cement in the form. of a solution in hexane or the like. Also, the present epoxides have a sufficiently high molecular weight and Example 3 a sufficiently high boiling point so that they do not boil away at temperatures normally encountered in EPDM saturat d EPDM, as d s rib d in EXampl 1, in the recovery and processing. form of a hexane solution (cement) was washed twice The following examples, in which all quantities are exwith distilled water in a Waring Blendorseparating the pressed by weight, will serve to illustrate the practice cement from the water after each washing. The washed of the invention in more detail. The EPDM polymers used cement was stabilized with 1 phr. Polygard and divided in the invention were made with vanadium oxytrichlorideinto two portions. Paraplex G-62 (1 phr.) Was added ethylaluminum sesquihalide catalyst. Traces of catalyst to one portion and the other portion was not treated so or residues thereof were believed to be present in the 88 Serve s a COIltfOl- T p e W fi at polymers. by allowing the solvent to evaporate. The solid rubber Example 1 samples were then heat aged in an oven set at 350 F. This example illustrates the enhancement of the anti- 2583 2 ,23 results of this Study are tabulated m the oxidant properties of a tris(alkylphenyl) phosphite by means of epoxidized soy bean oil when the epoxide is 30 added in conjunction with the phosphite to washed EPDM cement. Three samples of unsaturated EPDM polymer TABLE HI (e.g., a terpolymer containing ethylene/propylene in 45 weightratio and dicyclopentadiene; iodine number, 40 Sample Amount Additives (phr') gfilr ii est figfi 10; intrinsic viscosity in tetralin at 135 C., 2.5) each 1 Hr. at 350 F. stabilized differently as shown in Table 1, below, and a Polygamy, Paraplex control sample containing no stabilizer, were heat aged at C. for 16, 24 and 48 hours. The percent gel in ggg i8 kg Eggthe polymer was determined, with the results shown in Table I. 49

TABLE I Amounts of Additives (phn) Percent Gel After Heat Aging at 130 C. Sample Polygard Paraplex fort-ris(nonyl- G-62" phenyl) epoxidized OHrs. 16Hrs. 24Hrs. 48 Hrs. phosphite soy bean oil None None 17. 7 71.1 72.1

1. 0 None 20. 0 42. 2 63.1 80.5 0.5 1.0 24.9 29.2 18.3 70.9

1 Res'mified.

The tris(nonylphenyl)phosphite employed (Poly- Example 4 saturated EPDM as determined by oxygen absorption. This clearly established finding of synergism of antioxidant combinations in unsaturated compounds, as shown in Table IV below, is indeed extraordinary. All samples in this example were prepared separately from a single drum of washed ethylene-propylene-dicyclopentadiene terpolymer rubber cement containing no other stabilizer. The polymer had 62% ethylene, iodine number 11.6, no gel in cyclohexane, intrinsic viscosity in tetralin at C. 2.2. The phosphite and epoxide were added to the rubber cement; samples were dried at room temperature in air. The figure tabulated in Table IV as T is the time in minutes to absorb 20 m1. of oxygen per gram of polymer at 150 C. in an atomsphere of oxygen, and is a direct measure of stability.

TABLE 1V.INTERACTION OF TRIS (ALKYLPHENYL) PHOSPHITE AND EPOXY COMPOUND Additives (phr.) Absorption Time It will be seen from Table IV that the epoxide alone has no appreciable effect on stability (Samples IV-F to IV-I), but in combination with Polygard (Samples IV- A to IV-D) there is a synergistic interaction.

Having thus described my invention, what I claim and desire to protect by Letters Patent is:

1. A composition comprising 100 parts by weight of an unsaturated, elastomeric terpolymer of ethylene, propylene and a copolymerizable nonconjugated diene, from 0.1 to 1.0 part by weight of a tri(a1kylphenyl) phosphite in which the alkyl group has from 8 to 30 carbon atoms and from 0.5 to 5.0 parts by weight of an expoxide selected from the group consisting of epoxidized soy bean oil and epoxidized esters of fatty acids having from 10 to 30 carbon atoms with alkanols having up to 10 carbon atoms, the amount of epoxide being from 50% to 500% of the weight of the phosphite.

2. A composition comprising 100 parts by Weight of an unsaturated, elastomeric terpolymer of ethylene, propylene and clicyclopentadiene, from 0.1 to 1.0 part by weight of a tri(alkylphenyl) phosphite in which the alkyl group has from 8 to 30 carbon atoms and from 0.5 to 5.0 parts by weight of epoxidized soy bean oil, the amount of epoxidized soy bean oil being from 50%to 500% of the weight of the phosphite.

3. A composition comprising 100 parts by weight of an unsaturated, elastomeric terpolymer of ethylene, propylene, and dicyclopentadiene, from 0.1 to 1.0 part by weight of a tn'(alkylphenyl) phosphite in which the alkyl group has from 8 to 30 carbon atoms and from 0.5 to 5.0 parts by weight of an epoxidized ester of a fatty acid having from 10 to 30 carbon atoms with an alkanol having up to 10 carbon atoms, the amount of epoxidized ester being from to 500% of the weight of the phosphite.

4-. A composition comprising parts by weight of an unsaturated, elastomeric teipolymer of ethylene, propylene and dicyclopentadiene, from 0.1 to 1.0 part by weight of tri(nonylphenyl) phosphite and from 0.5 to 5.0 parts by weight of an epoxide selected from the group consisting of epoxidized soy bean oil and expoxidized esters of fatty acids having from 10 to 30 carbon atoms with alkanols having up to 10 carbon atoms, the amount of epoxide being from 50% to 500% of the Weight of the phosphite.

5. A composition comprising 100 parts by weight of an unsaturated, elastomeric terpolymer of ethylene, propylene and dicyclopentadiene, from 0.1 to 1.0 part by weight of tri(nonylphenyl) phosphite and from 0.5 to 5.0 parts by weight of epoxidized soy bean oil, the amount of epoxidized soy bean oil being from 50% to 500% of the weight of the phosphite.

6. A composition comprising 100 parts by weight of an unsaturated, elastomeric terpolymer of ethylene, propylene and dicyclopentadiene, from 0.1 to 1.0 part by weight of tri(nonylphenyl) phosphite and from 0.5 to 5.0 parts by weight of an epoxidized ester of a fatty acid having from 10 to 30 carbon atoms with an alkanol having up to 10 carbon atoms, the amount of epoxidized ester being from 50% to 500% of the weight of the phosphite.

References (Iited UNITED STATES PATENTS 3,132,027 5/ 1964 Norton et al. 99169 3,244,661 4/1966 Kline 260-29.7 3,244,662 4/1966 Strauss et a1 260-29.7

DONALD E. CZAJA, Primary Examiner.

R. A. WHITE, Assistant Examiner. 

1. A COMPOSITION COMPRISING 100 PARTS BY WEIGHT OF AN UNSATURATED, ELASTOMERIC TERPOLYMER OF ETHYLENE, PROPYLENE AND A COPOLYMERIZABLE NONCONJUGATED DIENE, FROM 0.1 TO 1.0 PART BY WEIGHT OF A TRI(ALKYLPHENYL) PHOSPHITE IN WHICH THE ALKYL GROUP HAS FROM 8 TO 30 CARBON ATOMS AND FROM 0.5 TO 5.0 PARTS BY WEIGHT OF AN EXPOXIDE SELECTED FROM THE GROUP CONSISTING OF EPOXIDIZED SOY BEAN OIL AND EPOXIDIZED ESTERS OF FATTY ACIDS HAVING FROM 10 TO 30 CARBON ATOMS WITH ALKANOLS HAVING UP TO 10 CARBON ATOMS, THE AMOUNT OF EPOXIDE BEING FROM 50% TO 500% OF THE WEIGHT OF THE PHOSPHITE. 